Back started his career at Nottingham and made his England debut in 1994, against Scotland at Murrayfield. He would only play another four games in the next two years and was often dismissed as being too small for international rugby.

Early in his career at his new club Leicester, Back was on the losing side in the 1996 Pilkington Cup final defeat to Bath. After the final whistle blew, he lashed out at what he thought was an opponent, but struck referee Steve Lander and received a six month ban.

On his return to rugby he received a call up to the British & Irish Lions tour of South Africa in 1997 and made an impact as a replacement in the victorious second Test.
After the tour he became a regular in the England back-row alongside Lawrence Dallaglio and Richard Hill.

In 2001 he scored in Leicester's nail-biting victory over Stade Francais in the Heineken Cup final and went on to play for the Lions in Australia. The following autumn Back captained England in the absence of Martin Johnson and led the side to a famous Cook Cup victory over Australia, winning 21-15.

In 2002 he won the Heineken Cup once again but illegally hit the ball out of Munster scrum-half Peter Stringer's grip as the Irishman put the ball into the scrum in the dying moments.

Back's storied career reached its peak in 2003 when he won the Rugby World Cup, playing an integral part in England's march to the title. He lost his place in the England set up the year after and decided to retire from England duty as the World Cup winning side started to break up.

In 2005 Clive Woodward talked him out of international retirement to play for the Lions against New Zealand. At 36 he became the oldest Lion and played in the first Test defeat. He did not play another Test on tour and that became his last top flight appearance, bringing the curtain down on an illustrious playing career.

Since his retirement Back has gone into coaching, beginning with Leicester and moving on to Leeds, where he was head coach as they gained promotion to the Premiership in 2009. Along with director of rugby Andy Key he kept the side in the top flight against the odds the following year, but walked away in May 2011 after failing to repeat the achievement.